1. Technical Field of the Invention
The present invention relates to an optical disc apparatus for writing data and/or reading data by use of a laser beam, and more particularly to a laser driving technique.
2. Description of the Related Art
As the write speed of an optical disc apparatus increases, its writing power must be increased, which requires an increase in the intensity of the laser beam emitted by the laser diode. This can be achieved by increasing the drive voltage applied to the laser diode. Without special arrangement, an increase in the drive voltage for the laser diode results in a reduction in the drive voltage applied to the laser drive circuit if the power supply voltage is constant. To prevent this, conventional optical disc apparatuses include a booster circuit connected between the power supply and the laser drive circuit to control the drive voltage for the laser drive circuit so that it always exceeds a predetermined level.
Prior art techniques for controlling the drive voltage for the laser drive circuit include, for example, those described in Japanese Patent Laid-Open Nos. 2003-168232 and 2003-78202. Specifically, Japanese Patent Laid-Open No. 2003-168232 discloses an optical disc apparatus adapted to maintain the intensity of its laser beam at a constant level. This optical disc apparatus includes a laser beam emitting means (or laser diode) for emitting a laser beam and a drive means (or laser drive circuit) for driving the laser beam emitting means, wherein the intensity of the laser beam emitted from the laser beam emitting means is detected and the power supply voltage of the drive means is adjusted based on the detection result. On the other hand, Japanese Patent Laid-Open No. 2003-78202 discloses a semiconductor laser drive circuit (or a laser drive circuit) for driving a plurality of semiconductor laser devices (or laser diodes) having different operating voltages one at a time. This laser drive circuit includes a power supply for generating different level power supply voltages each corresponding to one of the operating voltages of the above semiconductor laser devices, wherein the laser drive circuit drives each semiconductor laser device by applying the power supply voltage corresponding to the operating voltage of the semiconductor laser device.